1. Field of the Invention
The invention relates to a display device provided with a display screen which can display a character, a still image, a moving image, or the like, and relates to a technique for improving visibility of a display screen in various operating environments.
2. Description of the Related Art
A variety of electric appliances with a display screen structured by a liquid crystal panel, including a cell-phone, are prevalent. A liquid crystal panel has characteristics of being thin and light, and mobile laptop personal computers provided with a liquid crystal panel are produced. Furthermore, terminal devices called PDA (Personal Digital Assistant) are produced in large numbers, and becoming common.
As for display panels used in this way, not limited to a liquid crystal panel, the visual image quality is regarded as important, and panels provided with a function of adjusting the brightness and contrast automatically or manually are widely prevalent. For example, a liquid crystal display panel provided with an adjusting function which improves the visibility between one tone and another tone by changing transmission of the liquid crystal, without increasing luminance of a backlight of the liquid crystal panel is known (Reference 1: Japanese Patent Laid-Open No. 2003-186455).